Engine starting control apparatus

ABSTRACT

An engine starting control apparatus is basically provided with a motor control section, a valve timing control section and a start control section. The motor control section is configured to operate an electric motor to crank an engine with an output of the electric motor being adjustable. The valve timing control section is configured to operate a variable valve operating mechanism when the engine is started to change at least a close timing of an intake valve of the engine from an initial timing to a start timing such that the start timing is set closer to an intake bottom dead center during a single engine start as compared to the initial timing. The start control section is configured to adjust the output of the electric motor as the close timing of the intake valve changes from the initial timing to the start timing during the single engine start.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 11/969,951 filed on Jan. 7, 2008, now pending. Theentire disclosure of U.S. patent application Ser. No. 11/969,951 ishereby incorporated herein by reference. This application claimspriority to Japanese Patent Application No. 2007-005947, filed on Jan.15, 2007. The entire disclosure of Japanese Patent Application No.2007-005947 is hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an engine starting control apparatus.More particularly, the present invention relates to an engine startingcontrol apparatus that suppresses consumption of an electric power by anelectric motor used to crank an engine when the engine is started.

2. Background Information

In a conventional engine starting system, an electric motor is operatedto crank the engine when the engine is started. One example of such aconventional engine starting system is disclosed in Japanese Laid-OpenPatent Publication No. 2005-240768. In this publication, the startingperformance of an engine is improved by controlling the valve timing toa timing suitable for starting the engine (hereinafter called the “starttiming”). With the engine starting system disclosed in this publication,when the engine is started, the valve timing is controlled to the starttiming and fuel is prohibited from being supplied to the engine untilthe start timing is attained.

In view of the above, it will be apparent to those skilled in the artfrom this disclosure that there exists a need for an improved enginestarting control apparatus. This invention addresses this need in theart as well as other needs, which will become apparent to those skilledin the art from this disclosure.

SUMMARY OF THE INVENTION

With the conventional engine starting system described in theabove-mentioned publication, the engine is cranked solely by theelectric motor during the period prior to when the valve timing reachesthe start timing, i.e., during the period when the valve timing ischanging. Consequently, the battery consumption (electric powerconsumption) of the electric motor is inevitably larger during suchperiod. Moreover, since friction increases at lower temperatures, thebattery consumption of the electric motor is even larger and there isthe possibility that the battery power will become insufficient when thetemperature is low.

The present invention was conceived in view of the problem describedabove regarding the battery power. One object is to provide an enginestarting control apparatus that controls at least a close timing of anintake valve of an engine to a prescribed close timing that is suitablefor starting the engine when the engine is started, and to effectivelycurb the electric power consumption (battery consumption) of an electricmotor during starting while still ensuring good starting performance.

In order to achieve the above object of the present invention, an enginestarting control apparatus basically comprises a motor control section,a valve timing control section and a start control section. The motorcontrol section is configured to operate an electric motor to crank anengine with an output of the electric motor being adjustable. The valvetiming control section is configured to operate a variable valveoperating mechanism when the engine is started to change at least aclose timing of an intake valve of the engine from an initial timingcorresponding to a state in which the engine is stopped to a starttiming for starting the engine. The valve timing control sectionoperates the variable valve operating mechanism to set the close timingof the intake valve such that the start timing is set to be closer to anintake bottom dead center during a single engine start as compared tothe initial timing. The start control section is configured to adjustthe output of the electric motor as the close timing of the intake valvechanges from the initial timing to the start timing during the singleengine start.

These and other objects, features, aspects and advantages of the presentinvention will become apparent to those skilled in the art from thefollowing detailed description, which, taken in conjunction with theannexed drawings, discloses preferred embodiments of the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the attached drawings which form a part of thisoriginal disclosure:

FIG. 1 is a schematic view of an engine provided with an engine startingcontrol apparatus in accordance with an embodiment of the presentinvention;

FIG. 2 is a flowchart showing a start control executed by the enginestarting control apparatus in accordance with the illustrated embodimentof the present invention;

FIG. 3 is a simplified diagram illustrating an example of how a targetcranking rotational speed is set in the engine starting controlapparatus in accordance with the illustrated embodiment of the presentinvention;

FIG. 4 is a simplified diagram illustrating the relationships among aopen/close timing of intake valves, an engine torque, and a motor torqueduring cranking at the target cranking rotational speed in accordancewith the illustrated embodiment of the present invention;

FIG. 5 is a simplified diagram illustrating an example of a conversiontable of the motor torque versus the open/close timing of the intakevalves used by the engine starting control apparatus in accordance withthe illustrated embodiment of the present invention;

FIG. 6 is a time chart illustrating the start control executed by theengine starting control apparatus in accordance with the illustratedembodiment of the present invention;

FIG. 7 is a time chart for explaining the effects obtained by the enginestarting control apparatus in accordance with the illustrated embodimentof the present invention;

FIG. 8A is a schematic diagram illustrating a change in the open/closetiming of the intake valves in accordance with the illustratedembodiment of the present invention;

FIG. 8B is a simplified diagram illustrating the relationships among theopen/close timing of the intake valve, the motor torque and the enginetorque in accordance with the illustrated embodiment of the presentinvention;

FIG. 9A is a schematic diagram illustrating a change in the open/closetiming of the intake valve in accordance with a first modifiedembodiment of the present invention;

FIG. 9B is a simplified diagram illustrating the relationships among theopen/close timing of the intake valve, the motor torque and the enginetorque in accordance with the first modified embodiment of the presentinvention;

FIG. 10A is a schematic diagram illustrating a change in the open/closetiming of the intake valve in accordance with a second modifiedembodiment of the present invention; and

FIG. 10B is a simplified diagram illustrating the relationships amongthe open/close timing of the intake valve, the motor torque and theengine torque in accordance with the second modified embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Selected embodiments of the present invention will now be explained withreference to the drawings. It will be apparent to those skilled in theart from this disclosure that the following descriptions of theembodiments of the present invention are provided for illustration onlyand not for the purpose of limiting the invention as defined by theappended claims and their equivalents.

Referring initially to FIG. 1, an engine 10 provided with an enginestarting control apparatus in accordance with one embodiment of thepresent invention is illustrated. As shown in FIG. 1, the engine 10includes a crankshaft 12 that is connected to an electric motor 16through a power transmitting mechanism 14 comprising some gears. Theelectric motor 16 is connected to a battery 20 through a voltage varyingdevice 18. The electric motor 16 is configured and arranged to be drivento crank the engine 10 when the engine 10 is started. The voltagevarying device 18 is configured and arranged to adjust the output of theelectric motor 16 by varying the voltage supplied to the electric motor16 from the battery 20. In other words, the electric motor 16 isarranged such that the output from the electric motor 16 is adjustableto an output value ranging from a minimum output to a maximum output ofthe electric motor 16 by varying the voltage supplied to the voltagevarying device 18.

The engine 10 has a plurality of intake valves 22 and a plurality ofexhaust valves 24 as shown in FIG. 1. Each of the intake valves 22 iscoupled to an intake cam 28. The intake cams 28 are coupled to an intakecamshaft 26 that is arranged to rotate in coordination with thecrankshaft 12. Thus, the intake valves 22 are opened and closed by theintake cams 28 as the intake camshaft 26 rotates. Similarly, each of theexhaust valves 24 is coupled to an exhaust cam 32. The exhaust cams 32are coupled to an exhaust camshaft 30 that is arranged to rotate incoordination with the crankshaft 12. Thus, the exhaust valves 24 areopened and closed by the exhaust cams 32 as the exhaust camshaft 30rotates.

The engine 10 also includes a valve timing control device (VTC) 34serving as a variable valve operating mechanism. The VTC 34 is mountedto one end of the intake camshaft 26 (leftward end in FIG. 1). In thisillustrated embodiment, the VTC 34 is preferably configured and arrangedto vary the open/close timing (i.e., both the open timing and the closetiming) of the intake valves 22 by changing the rotational phase of theintake camshaft 26 with respect to the crankshaft 12. This type of VTC34 is well-known in the art. For example, Japanese Laid-Open PatentPublication No. 2005-240768 discloses this type of VTC. Since the VTC 34is well known in the art, the structure thereof will not be discussed orillustrated in detail herein. Rather, it will be apparent to thoseskilled in the art from this disclosure that the components can be anytype of structure and/or programming that can be used to carry out thepresent invention.

The engine 10 further includes an electronic control unit (ECU) 40. TheECU 40 is configured to determine the engine operating conditions basedon input signals from various sensors to control the operation of theengine 10, the voltage varying device 18 (electric motor 16), and theVTC 34 accordingly. In particular, when the engine 10 is started, theECU 40 is configured to control the voltage varying device 18 such thata prescribed voltage is supplied to the electric motor 16 to crank theengine 10. At the same time, the ECU 40 is configured to control the VTC34 such that the open/close timing of the intake valves 22 is adjustedto a timing (start timing) suited to starting the engine 10.

The ECU 40 preferably includes a microcomputer with an engine startingcontrol program that controls the operation of the engine 10, thevoltage varying device 18, and the VTC 34 as discussed below. The ECU 40can also include other conventional components such as an inputinterface circuit, an output interface circuit, and storage devices suchas a ROM (Read Only Memory) device and a RAM (Random Access Memory)device. The memory circuit stores processing results and controlprograms that are run by the processor circuit. The ECU 40 isoperatively coupled to the various components of the engine 10 in aconventional manner. The internal RAM of the ECU 40 stores statuses ofoperational flags and various control data. The internal ROM of the ECU40 stores the preset map and data for various operations. The ECU 40 iscapable of selectively controlling any of the components of the controlsystem in accordance with the control program. It will be apparent tothose skilled in the art from this disclosure that the precise structureand algorithms for the ECU 40 can be any combination of hardware andsoftware that will carry out the functions of the present invention. TheECU 40 preferably constitutes a controller including a motor controlsection, a valve timing control section and a start control section inaccordance with the illustrated embodiment of the present invention.

The input signals fed to the ECU 40 include a detection signal from anair flow meter (not shown) configured and arranged to detect an intakeair flow rate, a detection signal from a throttle sensor (not shown)configured and arranged to detect a throttle opening degree, a detectionsignal from an accelerator sensor (not shown) configured and arranged todetect an accelerator operation amount, a detection signal from a cranksensor 42 (crank angle detecting section) configured and arranged todetect a rotational angle of the crankshaft 12, a detection signal froma cam sensor 44 (cam angle detecting section) configured and arranged todetect a rotational angle of the intake camshaft 26, a detection signalfrom a battery sensor 46 configured and arranged to detect a voltage orcurrent of the battery 20, a detection signal from a coolant temperaturesensor 48 configured and arranged to detect a temperature of an enginecoolant, and on-off signals from such switches as an ignition key switchand an idle switch.

The ECU 40 is configured to calculate an engine speed Ne based on thedetection signal from the crank sensor 42 (e.g., based on a referencefrequency of the crank angle signal). The ECU 40 is configured to detectthe open/close timing of the intake valves 22 as a rotational phase ofthe intake camshaft 26 with respect to the crankshaft 12 based on thedetection signals from the crank sensor 42 and the cam sensor 44. Ofcourse, it will be apparent to those skilled in the art from thisdisclosure that the invention is not limited to determining the enginespeed Ne and the open/close timing of the intake valves 22 based on theinput signals mentioned here. It is acceptable to determine (i.e.,detect or estimate) the engine speed Ne and the open/close timing of theintake valves 22 based on input signals from other sensors.

The engine starting control executed by the ECU 40 in the illustratedembodiment will now be explained.

In the engine starting control of the illustrated embodiment, the ECU 40is configured to operate the electric motor 16 to crank the engine 10when the engine 10 is started. The ECU 40 is also configured to operatethe VTC 34 to change the open/close timing of the intake valves 22 froma timing (initial timing) corresponding to an initial state in which theengine 10 is stopped to the start timing that is suitable for startingthe engine 10. During the cranking of the engine 10, the open/closetiming of the intake valves 22 is detected as the open/close timingchanges from the initial timing to the start timing, and the torque ofthe electric motor 16 is controlled based on the detected open/closetiming.

When the VTC 34 is used as the variable valve operating mechanism as inthe illustrated embodiment, the open/close timing of the intake valves22 is generally set to a maximally retarded timing, i.e., the mostretarded timing possible, when the engine 10 is stopped (i.e., in aninitial state of the starting process). Thus, in the illustratedembodiment, the initial timing of the open/close timing of the intakevalves 22 is defined as the most retarded timing of the open/closetiming of the intake valves 22. With the most retarded timing, the closetiming (IVC) of the intake valves 22 is greatly retarded relative to thebottom dead center (BDC) position of the intake stroke (i.e., intakebottom dead center) and the engine torque produced by the ignition offuel is small. By controlling the timing of the intake valves 22 to thestart timing (i.e., the timing suitable for starting the engine 10), theopen/close timing of the intake valves 22 is advanced closer to BDC, andthus, the engine torque increases. Thus, as the open/close timing of theintake valves 22 approaches the start timing, a state is achieved inwhich a prescribed cranking rotational speed is maintained even if thetorque of the electric motor 16 is reduced. Therefore, in theillustrated embodiment of the present invention, the electric motor 16is controlled to output only the amount of torque necessary to maintainthe prescribed cranking rotational speed in conjunction with the enginetorque by controlling the torque of the electric motor 16 based on theopen/close timing of the intake valves 22. Accordingly, the electricpower consumption (battery consumption) of the electric motor 16 can besuppressed.

FIG. 2 is a flowchart showing the engine starting control executed bythe ECU 40 in accordance with the illustrated embodiment.

In step S11 of the flowchart shown in FIG. 2, the ECU 40 is configuredto determine if the engine starting control is required to be commenced.This determination is accomplished based on, for example, the state ofthe on-off signal of the ignition key switch. If the ignition key switchis on in step S11 (Yes in step S11), then the ECU 40 determines that thestart control is required to be commenced and proceeds to step S12.

In step S12, the ECU 40 is configured to start cranking the engine 10.In other words, the ECU 40 is configured to control the voltage varyingdevice 18 such that a prescribed voltage is supplied to the electricmotor 16 to drive the electric motor 16 with a constant output. Theprescribed voltage is a voltage value sufficient to produce a torquethat is at least large enough to balance against the friction torquethat exists at a target cranking rotational speed. The prescribedvoltage is set, for example, in accordance with the engine coolanttemperature Tw. Furthermore, the target cranking rotational speed is anengine speed at which the engine 10 can reliably accomplish ignition andcombustion. For example, the target cranking rotational speed can be setbased on an ignition characteristic of the engine 10 by referring to amap such as the one shown in FIG. 3 so as to achieve an engine speed atwhich the compression temperature inside the cylinder reaches or exceedsa prescribed temperature. As a result, the engine speed (crankingrotational speed) approaches the target cranking rotational speed. Theoperation executed in step S12 corresponds to the motor control sectionof the illustrated embodiment of the present invention.

In step S13, the ECU 40 is configured to execute an engine start valvetiming control. In other words, the ECU 40 is configured to operate theVTC 34 such that the open/close timing of the intake valves 22 iscontrolled from the most retarded timing (initial timing) correspondingto a state in which the engine 10 is stopped to the start timing. Theoperation executed in step S13 corresponds to the valve timing controlsection of the illustrated embodiment of the present invention.

When the engine start valve timing control commences, the open/closetiming of the intake valves 22 does not normally reach the start timingright away. Instead, the open/close timing of the intake valves 22gradually changes toward the start timing. During the period when theintake valve open/close timing is changing, the electric power consumedby the electric motor 16 will be large if the engine 10 is cranked bythe electric motor 16 alone. Moreover, if the VTC 34 is hydraulicallydriven, then the amount of time required for the open/close timing ofthe intake valves 22 to reach the start timing will be longer when thetemperature is low because it takes time for the hydraulic pressure torise at low temperatures. Additionally, since the friction of the engine10 increases at low temperatures, the electric power consumption of theelectric motor 16 will be higher and there will be the possibility thatthe power of the battery 20 will become insufficient when thetemperature is low. One way to prevent the power of the battery 20 frombecoming insufficient is to increase the size of the battery, but thereare many cases in which layout considerations prohibit increasing thesize of the battery 20. Moreover, increasing the size of the battery 20increases the cost.

On the other hand, since the engine 10 produces torque when fuelignition occurs, the target cranking rotational speed can be maintainedafter fuel ignition begins even if the torque of the electric motor 16is lowered by an amount corresponding to the engine torque produced dueto the fuel combustion. The torque produced by the engine 10 changes(increases) in accordance with a change in the open/close timing of theintake valves 22.

Therefore, in the illustrated embodiment, the ECU 40 is configured todetect an occurrence of fuel ignition in the engine 10, and to controlthe torque of the electric motor 16 in accordance with the actualopen/close timing of the intake valves 22 after fuel ignition occurs inorder to suppress the electric power consumption of the electric motor16.

Accordingly, in step S14, the ECU 40 is configured to determine if fuelignition has occurred in the engine 10. The determination executed instep S14 regarding ignition is accomplished by, for example, determiningif the engine speed has reached the target cranking rotational speed. Asexplained previously, the target cranking rotational speed is set basedon the ignition and combustion characteristics of the engine 10 as shownin FIG. 3. Thus, when the engine 10 reaches the target crankingrotational speed, it is reasonable to assume that the engine 10 hasachieved ignition of the fuel. Thus, if the engine speed has reached thetarget cranking rotational speed, then the ECU 40 determines that theengine 10 is igniting the fuel and proceeds to step S15. If the enginespeed is lower than the target cranking rotational speed, then the ECU40 continues operating the electric motor 16 at the constant outputtorque.

Alternatively, in order to determine the occurrence of fuel ignitionmore accurately, it is acceptable to set an ignition determiningrotational speed as a threshold speed that is separate from the targetcranking rotational speed. For example, it is feasible to set theignition determining rotational speed to a value 5 to 10% larger thanthe target cranking rotational speed. It is also acceptable to determineif ignition is occurring based on parameters other than the enginespeed. For example, the temperature and pressure inside the cylinders ofthe engine 10 can be detected (or estimated) and the ignitiondetermination can be accomplished based on the detected (or estimated)temperature and pressure inside the cylinders.

In step S15, the ECU 40 is configured to start a torque control (motortorque control) of the electric motor 16. In other words, the ECU 40 isconfigured to detect the open/close timing of the intake valves 22 basedon the detection signals from the crank sensor 42 and the cam sensor 44.The ECU 40 is then configured to control the output (torque) of theelectric motor 16 based on the detected open/close timing. The operationexecuted in step S15 corresponds to the start control section of theillustrated embodiment of the present invention.

Alternatively, since the open/close timing of the intake valves 22 andthe center phase of the operating angle (i.e., a duration between theopen timing and the close timing in terms of the crank angle) of theintake valves 22 change in synchronization with each other, it isacceptable to estimate the open/close timing of the intake valves 22 bydetecting the center phase of operation angle of the intake valves 22and to control the output of the electric motor 16 based on theestimated open/close timing of the intake valves 22.

As explained previously, ignition of the fuel causes the engine 10 toproduce torque and the engine torque produced by the fuel ignitionincreases as the open/close timing of the intake valves 22 approachesthe start timing. Thus, as shown in FIG. 4, as the open/close timing ofthe intake valves 22 draws closer to the start timing (i.e., as theopen/close timing advances in the illustrated embodiment), less torqueis required from the electric motor 16 in order to maintain the targetcranking rotational speed. In other words, the torque that the electricmotor 16 needs to generate during cranking at the target crankingrotational speed decreases as the open/close timing of the intake valves22 advances.

Therefore, in the illustrated embodiment of the present invention, atable plotting the motor torque versus the valve timing (intake valveopen/close timing) such as the one shown in FIG. 5 is prepared inadvance. The ECU 40 is configured to determine the motor torque based onthe actual open/close timing of the intake valves 22 detected based onthe detection signals from the crank sensor 42 and the cam sensor 44 byreferring to the table such as the one shown in FIG. 5. During theremaining period when the engine 10 is being cranked at the targetcranking rotational speed, the ECU 40 is configured to control theelectric motor 16 to output the motor torque according to the table suchas the one shown in FIG. 5. More specifically, the output of theelectric motor 16 is controlled by controlling the voltage supplied tothe electric motor 16 using the voltage varying device 18. As a result,after fuel ignition started in the engine 10, the torque of the electricmotor 16 decreases as the open/close timing of the intake valves 22approaches (advances toward) the start timing, and the rotational speedof engine 10 is held at the target cranking rotational speed by bothtorque from the electric motor 16 and torque produced by the engine 10due to fuel combustion.

In step S16, the ECU 40 is configured to determine if full combustionhas been achieved in the engine 10. The determination regarding fullcombustion is made, for example, by determining if the engine speed Nehas reached a preset full combustion determining rotational speed (whichis larger than the target cranking rotational speed). When the enginespeed Ne has reached the full combustion determining rotational speed,the open/close timing of the intake valves 22 is at the start timing andit is feasible to assume that the engine 10 is producing a sufficientamount of torque. If the engine speed Ne is equal to or larger than thefull combustion determining rotational speed in step S16, then the ECU40 proceeds to step S17. If the engine speed Ne is not equal to orlarger than the full combustion determining rotational speed in stepS16, then the ECU 40 continues the torque control of the electric motor16.

The full combustion determination is not limited to this methodexplained herein. It is also acceptable to detect (or estimate) thetemperature and pressure inside the cylinders of the engine 10 anddetermine if full combustion has been achieved based on the detected (orestimated) temperature and pressure inside the cylinders.

In step S17, the ECU 40 is configured to stop the electric motor 16.Then, the ECU 40 ends the engine starting control.

FIG. 6 is a time chart for the engine starting control in accordancewith the illustrated embodiment.

When the engine starting control begins, the prescribed voltage issupplied to the electric motor 16 from the voltage varying device 18 andthe electric motor 16 is operated at constant output to start crankingthe engine 10 (time t1). When cranking commences, the VTC 34 is drivenand the open/close timing of the intake valves 22 is controlled tochange from the initial timing (the most retarded timing correspondingto when the engine 10 is stopped) to the start timing. However, if thetemperature is low such that the friction is large and if the VTC 34 isa hydraulically driven valve timing control device, then it will taketime for the hydraulic pressure to rise and the open/close timing of theintake valves 22 will not reach the start timing immediately. When fuelignition starts to occur in the engine 10, the ECU 40 is configured tostart the torque control (motor torque control) of the electric motor 16(time t2). Since ignition of fuel causes the engine 10 to produce atorque, after fuel ignition occurred at time t2, the torque of theelectric motor 16 is decreased by the amount of engine torque produced.When the VTC 34 has been driven long enough for the hydraulic pressureto rise, the open/close timing of the intake valves 22 starts to changefrom the most retarded timing towards the start timing (time t3).

The engine torque resulting from the fuel ignition in the engine 10increases as the open/close timing of the intake valves 22 approachesthe start timing (i.e., advances toward the start timing in theillustrated embodiment). By controlling the voltage supplied to theelectric motor 16 (i.e., decreasing the output of the electric motor 16)in accordance with the (actual) open/close timing of the intake valves22, the torque of the electric motor 16 is decreased as the enginetorque increases. When the engine 10 reaches full combustion, theelectric motor 16 is stopped (time t4). As a result, an amount ofelectric power (torque) corresponding to the hatched region shown inFIG. 6 is conserved during engine cranking in the illustrated embodimentas compared to when the output of the electric motor 16 is maintained atconstant output.

FIG. 6 illustrates an example in which the point in time when theelectric motor 16 is stopped is coincident with the point in time whenthe open/close timing of the intake valves 22 reaches the start timing(i.e., both occur at the time t4). In other words, the electric motor 16is stopped when the open/close timing of the intake valves 22 reachesthe start timing. However, the invention is not limited to stopping theelectric motor 16 when the open/close timing of the intake valves 22reaches the start timing. More specifically, as explained above withreference to the flowchart of FIG. 2, the electric motor 16 can bestopped when it is determined that the engine 10 has achieved fullcombustion.

The effects that can be obtained with the engine starting controlapparatus in accordance with the illustrated embodiment will now beexplained.

The ECU 40 of the illustrated embodiment is configured to control theopen/close timing of the intake valves 22 of the engine 10 to the starttiming suited for starting the engine 10 when the engine 10 is started.In the illustrated embodiment, the open/close timing of the intakevalves 22 is detected and the torque of the electric motor 16 iscontrolled based on the detected open/close timing. In this way, thetorque of the electric motor 16 can be decreased in accordance with thechange (increase) in engine torque that results from changing theopen/close timing of the intake valves 22. As a result, the targetcranking rotational speed can be sustained without the electric motor 16consuming an excessive amount of electric power, and thus, a situationin which the electric power of the battery 20 becomes insufficient canbe prevented. This result enables cranking to be executed for a longerperiod of time without requiring a large size of the battery 20 andenables stable engine starting to be accomplished under low temperatureconditions.

Since the torque of the electric motor 16 is controlled based on theopen/close timing of the intake valves 22, the output of the electricmotor 16 (i.e., the voltage supplied to the electric motor 16) can beoptimized more quickly and the electric power consumption can besuppressed more effectively. Since the engine speed (cranking rotationalspeed) also increases as the engine torque increases, it would seemfeasible to use feedback control based on the engine speed. However, asshown in FIG. 7, controlling the torque of the electric motor 16 basedon the open/close timing of the intake valves 22 in accordance with theillustrated embodiment (indicated with solid line) enables the motortorque to respond more quickly to the increase in the engine torque thanusing feedback control of the motor torque based on the engine speed(indicated with single-dot chain line). More specifically, when themotor torque is controlled with feedback control based on the enginerotational speed, the output of the electric motor 16 is controlledafter the engine speed increases. Consequently, there is a delay in themotor torque control when the feedback control is executed based on theengine speed, and thus, the electric power consumption becomes larger ascompared to the engine starting control of the illustrated embodiment byan amount corresponding to the torque region indicated with hatching inFIG. 7. Thus, since the output of the electric motor 16 can becontrolled before the engine speed actually rises in the illustratedembodiment, the engine starting control of the illustrated embodiment issuperior to feedback control based on the engine speed from thestandpoint of reducing the electric power consumption of the electricmotor 16 as shown in FIG. 7.

In the illustrated embodiment explained above, the open/close timing ofthe intake valves 22 is changed by changing the rotational phase of theintake camshaft 26 with respect to the crankshaft 12. More specifically,as seen in the open/close timing diagram in FIG. 8A in accordance withthe illustrated embodiment, the initial timing of the open/close timingof the intake valves 22 is set to the most retarded timing and both theopen timing (IVO) and the close timing (IVC) of the intake valves 22 areadvanced from the initial timing (the most retarded timing) shown in thesolid lines in FIG. 8A to the start timing shown in the dotted lines inFIG. 8A. At the initial timing, the intake valve close timing (IVC) isgreatly retarded with respect to bottom dead center (BDC) as shown inFIG. 8A, and thus, the engine torque is small as shown in FIG. 8B. Asthe close timing (IVC) of the intake valves 22 advances toward bottomdead center, the engine torque increases as shown in FIG. 8B. Thus, inthe illustrated embodiment, as shown in FIG. 8B, the ECU 40 isconfigured to decrease the torque of the electric motor 16 as theopen/close timing of the intake valves 22 advances.

However, the present invention is not limited to changing the open/closetiming of the intake valves 22 as illustrated in FIGS. 8A and 8B. Inother words, the engine starting control apparatus in accordance withthe present invention can be carried out so long as at least the closetiming of the intake valves 22 of the engine 10 is controlled to a starttiming suited for starting the engine 10 when the engine 10 is started,and so long as the valve timing control is accompanied by a control ofthe torque (output) of the electric motor 16.

For example, FIGS. 9A and 9B illustrate a first modified embodiment inwhich the VTC 34 (variable valve operating mechanism) is configured andarranged to change the close timing of the intake valves 22 by changingthe amount of valve lift and the operating angle of the intake valves22. In the first modified embodiment illustrated in FIGS. 9A and 9B, theinitial state timing is defined as a timing where the valve lift amountand the operating angle of the intake valves 22 are the smallest asshown in the solid lines in FIG. 9A. In the initial state, the closetiming of the intake valve (IVC) is greatly advanced with respect tobottom dead center (BDC) of the intake stroke. As the valve lift amountand the operating angle increase, the intake valve close timing (IVC) isretarded until it reaches the start timing in the vicinity of bottomdead center. At the initial timing, the intake valve close timing (IVC)is greatly advanced with respect to bottom dead center, and thus, theengine torque is small as shown in FIG. 9B. As the valve lift amount andthe operating angle of the intake valves 22 are increased, the intakevalve close timing (IVC) retards toward bottom dead center, and thus,the engine torque increases as shown in FIG. 9B. Thus, with the firstmodified embodiment, as shown in FIG. 9B, the ECU 40 is configured todecrease the torque of the electric motor 16 as the valve lift amountand the operating angle increase.

On the other hand, FIGS. 10A and 10B illustrate a second modifiedembodiment in which the VTC 34 (variable valve operating mechanism) isconfigured and arranged to change the close timing of the intake valves22 by changing the amount of valve lift and the operating angle of theintake valves 22. In the second modified embodiment, the initial timingis defined as the timing where the valve lift and the operating angle ofthe intake valves 22 are the largest. In the initial state, the closetiming of the intake valve (IVC) is retarded with respect to bottom deadcenter (BDC) as shown in the solid lines in FIG. 10A. As the valve liftamount and the operating angle decrease, the intake valve close timingis advanced until it reaches a start timing in the vicinity of bottomdead center as shown in the dotted lines in FIG. 10A. At the initialtiming, the close timing (IVC) of the intake valves 22 is greatlyretarded with respect to bottom dead center, and thus, the engine torqueis small as shown in FIG. 10B. As the valve lift amount and theoperating angle are decreased, the intake valve close timing advancestoward bottom dead center, and thus, the engine torque increases asshown in FIG. 10A. Thus, with the second modified embodiment, as shownin FIG. 10B, the ECU 40 is configured to decrease the torque of theelectric motor 16 as the valve lift amount and operating angle decrease.

In the embodiments described above, the open/close timing of the intakevalves 22 is detected based on the detection signals from the cranksensor 42 and the cam sensor 44, and the output (torque) of the electricmotor 16 is controlled based on the detected open/close timing of theintake valves 22. However, the present invention is not limited to suchan arrangement. For example, since the engine start valve timing controlcauses the open/close timing of the intake valves 22 change graduallyfrom the initial timing to the start timing over time, it is possible tocontrol the output of the electric motor 16 based on the amount of timeelapsed since the engine start valve timing control commenced.

Additionally, although the variable valve operating mechanisms (VTC 34)presented in the embodiments described heretofore are configured tochange both the open timing and the close timing of the intake valves22, it is also feasible to employ a variable valve operating mechanismthat changes only the close timing of the intake valves 22.

With the illustrated embodiments of the present invention, the electricmotor 16 cranks the engine 10 when the engine 10 is started and theoutput of the electric motor 16 is changed as the open/closing timing ofthe intake valves 22 changes. The output torque of the electric motor 16is varied in accordance with the change in the engine torque thataccompanies the change in the open/close timing of the intake valves 22,and thus, the output torque of the electric motor 16 does not becomeexcessively insufficient. As a result, the target cranking rotationalspeed can be maintained while suppressing the electric power consumed bythe electric motor 16 as much as possible, thereby preventing theelectric power of the battery 20 from becoming insufficient. This resultenables cranking to be executed for a longer period of time withoutrequiring a larger battery and enables stable starting to beaccomplished under low temperature conditions.

Moreover, compared to other control schemes, e.g., changing the outputof the electric motor based on the engine speed, changing the output ofthe electric motor 16 based on the open/close timing of the intakevalves 22 as in the illustrated embodiments enables the output of theelectric motor 16 to be optimized more quickly and the power consumed bythe electric motor 16 to be suppressed more effectively.

GENERAL INTERPRETATION OF TERMS

In understanding the scope of the present invention, the term“comprising” and its derivatives, as used herein, are intended to beopen ended terms that specify the presence of the stated features,elements, components, groups, integers, and/or steps, but do not excludethe presence of other unstated features, elements, components, groups,integers and/or steps. The foregoing also applies to words havingsimilar meanings such as the terms, “including”, “having” and theirderivatives. Also, the terms “part,” “section,” “portion,” “member” or“element” when used in the singular can have the dual meaning of asingle part or a plurality of parts. The term “detect” as used herein todescribe an operation or function carried out by a component, a section,a device or the like includes a component, a section, a device or thelike that does not require physical detection, but rather includesdetermining, measuring, modeling, predicting or computing or the like tocarry out the operation or function. The term “configured” as usedherein to describe a component, section or part of a device includeshardware and/or software that is constructed and/or programmed to carryout the desired function.

While only selected embodiments have been chosen to illustrate thepresent invention, it will be apparent to those skilled in the art fromthis disclosure that various changes and modifications can be madeherein without departing from the scope of the invention as defined inthe appended claims. For example, the size, shape, location ororientation of the various components can be changed as needed and/ordesired. Components that are shown directly connected or contacting eachother can have intermediate structures disposed between them. Thefunctions of one element can be performed by two, and vice versa. Thestructures and functions of one embodiment can be adopted in anotherembodiment. It is not necessary for all advantages to be present in aparticular embodiment at the same time. Every feature which is uniquefrom the prior art, alone or in combination with other features, alsoshould be considered a separate description of further inventions by theapplicant, including the structural and/or functional concepts embodiedby such feature(s). Thus, the foregoing descriptions of the embodimentsaccording to the present invention are provided for illustration only,and not for the purpose of limiting the invention as defined by theappended claims and their equivalents.

What is claimed is:
 1. An engine starting control apparatus comprising:a motor control section configured to operate an electric motor to crankan engine with an output of the electric motor being adjustable; a valvetiming control section configured to operate a variable valve operatingmechanism when the engine is started to change at least a close timingof an intake valve of the engine from an initial timing corresponding toa state in which the engine is stopped to a start timing for startingthe engine, the valve timing control section operating the variablevalve operating mechanism to set the close timing of the intake valvesuch that the start timing is set to be closer to an intake bottom deadcenter during a single engine start as compared to the initial timing;and a start control section configured to continuously decrease theoutput of the electric motor as the close timing of the intake valvedraws closer to the start timing from the initial timing during thesingle engine start.
 2. The engine starting control apparatus as recitedin claim 1, wherein the start control section is further configured todetermine the close timing of the intake valve, and to decrease theoutput of the electric motor based on the close timing of the intakevalve determined.
 3. The engine starting control apparatus as recited inclaim 1, wherein the start control section is further configured todecrease the output of the electric motor after an occurrence of fuelignition in the engine is detected.
 4. The engine starting controlapparatus as recited in claim 1, wherein the start control section isfurther configured to decrease the output of the electric motor suchthat a cranking rotational speed of the engine is maintained at aprescribed rotational speed.
 5. The engine starting control apparatus asrecited in claim 1, wherein the start control section is furtherconfigured to decrease the output of the electric motor by varying avoltage supplied to the electric motor.
 6. The engine starting controlapparatus as recited in claim 2, further comprising a crank angledetecting section configured and arranged to detect a rotational angleof a crankshaft of the engine, and a cam angle detecting sectionconfigured and arranged to detect a rotational angle of an intakecamshaft of the engine, the start control section being furtherconfigured to determine the close timing of the intake valve based ondetection results from the crank angle detecting section and the camangle detecting section.
 7. The engine starting control apparatus asrecited in claim 1, wherein the start control section is furtherconfigured to decrease the output of the electric motor based on anamount of time elapsed since the valve timing control section startedoperating the variable valve operating mechanism to change the closetiming of the intake valve from the initial timing to the start timing.8. The engine starting control apparatus as recited in claim 1, whereinthe valve timing control section is further configured to operate thevariable valve operating mechanism to change the close timing from theinitial timing to the start timing by changing a valve lift amount andan operation angle of the intake valve.
 9. The engine starting controlapparatus as recited in claim 8, wherein the start control section isfurther configured to decrease the output of the electric motor as thevalve lift amount and the operation angle of the intake valve increase.10. The engine starting control apparatus as recited in claim 8, whereinthe start control section is further configured to decrease the outputof the electric motor as the valve lift amount and the operation angleof the intake valve decrease.
 11. The engine starting control apparatusas recited in claim 1, wherein the start control section is furtherconfigured to maintain the output of the electric motor at a constantoutput until an occurrence of fuel ignition in the engine is detected,and to decrease the output of the electric motor according to a changein the close timing of the intake valve after the occurrence of fuelignition in the engine is detected.
 12. An engine starting controlapparatus comprising: a motor control section configured to operate anelectric motor to crank an engine with an output of the electric motorbeing adjustable; a valve timing control section configured to operate avariable valve operating mechanism when the engine is started to changeat least a close timing of an intake valve of the engine from an initialtiming corresponding to a state in which the engine is stopped to astart timing for starting the engine, the valve timing control sectionoperating the variable valve operating mechanism to set the close timingof the intake valve such that the start timing is set to be closer to anintake bottom dead center during a single engine start as compared tothe initial timing; and a start control section configured to adjust theoutput of the electric motor as the close timing of the intake valvechanges from the initial timing to the start timing during the singleengine start, the start control section further adjusting the output ofthe electric motor by an adjustment value after the engine has beenstarted and during the time before perfect combustion has been achieved,the adjustment value being equal to an amount corresponding to enginetorque produced by initial fuel combustion.
 13. An engine startingcontrol method comprising: operating an electric motor to crank anengine with an output of the electric motor being adjustable; changingat least a close timing of an intake valve of the engine from an initialtiming corresponding to a state in which the engine is stopped to astart timing for starting the engine when the engine is started, suchthat the start timing is closer to an intake bottom dead center during asingle engine start as compared to the initial timing; and decreasingcontinuously the output of the electric motor as the close timing of theintake valve draws closer to the start timing from the initial timingduring the single engine start.
 14. An engine starting systemcomprising: an electric motor configured to crank an engine with anoutput of the electric motor being adjustable; a variable valve controlmechanism configured to control an intake valve of the engine; and acontroller including a motor control section configured to operate theelectric motor to crank the engine when the engine is started, a valvetiming control section configured to operate the variable valve controlmechanism when the engine is started to change at least a close timingof the intake valve from an initial timing corresponding to a state inwhich the engine is stopped to a start timing for starting the engine,the valve timing control section operating the variable valve controlmechanism to set the close timing of the intake valve such that thestart timing is set to be closer to an intake bottom dead center duringa single engine start as compared to the initial timing, and a startcontrol section configured to continuously decrease the output of theelectric motor as the close timing of the intake valve draws closer tothe start timing from the initial timing during the single engine start.15. An engine starting system comprising: an electric motor configuredto crank an engine with an output of the electric motor beingadjustable; a variable valve control mechanism configured to control anintake valve of the engine; and a controller including a motor controlsection configured to operate the electric motor to crank the enginewhen the engine is started, a valve timing control section configured tooperate the variable valve control mechanism when the engine is startedto change at least a close timing of the intake valve from an initialtiming corresponding to a state in which the engine is stopped to astart timing for starting the engine, the valve timing control sectionoperating the variable valve control mechanism to set the close timingof the intake valve such that the start timing is set to be closer to anintake bottom dead center during a single engine start as compared tothe initial timing, and a start control section configured to adjust theoutput of the electric motor as the close timing of the intake valvechanges from the initial timing to the start timing during the singleengine start, the start control section further adjusting the output ofthe electric motor by an adjustment value after the engine has beenstarted and during the time before perfect combustion has been achieved,the adjustment value being equal to an amount corresponding to enginetorque produced by initial fuel combustion.